Cystic Fibrosis: History, Pathology, and Molecular Treatments, and Genetic Mutations

Pre-1993 Treatment Landscape:
    * Before the release of the first pharmaceutical treatments in $1993$ , there were effectively no specialized drugs for cystic fibrosis.
    * During this period, individuals diagnosed with cystic fibrosis typically lived only into their late teens or early $20s$ .
    * Quality of life declined significantly as patients aged due to severe symptomatic issues, primarily involving persistent coughing and chronic mucus buildup.

Timeline and Identification:
    * Pulmozyme was developed throughout the late $1980s$ and early $1990s$ , with its official release occurring in $1993$ .
    * The drug is a form of DNase I.
    * As an enzyme (identified by the "-ase" suffix), its specific biological function is to break down DNA molecules by cleaving phosphodiester bonds.
    * The speaker references the historical context of Avery, McLeod, and McCarty, who were foundational in identifying DNA as the transforming principle.
Administration and Clinical Impact:
* Patients with cystic fibrosis inhale this enzyme as a pharmaceutical treatment.
* Following the introduction of Pulmozyme, the average life expectancy for individuals with cystic fibrosis increased to the early $30s$ and into the $40s$ .
Limitations of Treatment:
    * The speaker emphasizes that Pulmozyme is a symptomatic treatment rather than a curative one.
    * It does not address the underlying protein defect involving the CFTR protein.
    * While cystic fibrosis affects multiple organs (as noted in supplemental videos), Pulmozyme primarily treats the pulmonary (lung) symptoms.

The Role of CFTR and Water:
* In a healthy system, the CFTR transmembrane protein regulates the flow of ions, ensuring there is a necessary amount of water present for mucus to be moved by the action of cilia in the lungs.
* In cystic fibrosis, this protein is non-functional, leading to dehydration of the mucus and subsequent buildup.
Pathogens and Biofilm Formation:
    * The air we breathe is not sterile; it contains bacteria. A common and problematic pathogen for individuals with cystic fibrosis is Pseudomonas.
    * Pseudomonas can form biofilms, which are more than just clusters of growing bacteria.
    * Biofilms are held together by an "extracellular stuff" matrix composed of various molecules, one of the most critical being extracellular DNA.
Sources of Extracellular DNA:
    * DNA is released into the extracellular environment when cells die and lyse.
    * Some bacterial cells can actively secrete small DNA molecules.
    * The human immune system contributes to this; neutrophils enter the lungs to combat the bacteria, dying and releasing their own DNA in the process.
Pulmozyme Interaction:
* By inhaling the DNase enzyme, patients can break down the extracellular DNA holding the biofilm and thick mucus together. This makes it significantly easier for the patient to break up the mucus and expel it from the airway.

Genetic Diversity:
* Over the last $25$ to $30$ years, advances in DNA sequencing have allowed scientists to identify over $2500$ different mutations that can cause cystic fibrosis.
* Testing for these mutations is complex and expensive because DNA sequences must be meticulously analyzed against these thousands of known variations.
Population Statistics:
* The lecture focuses on specific columns of mutations that account for $98\%$ of the cystic fibrosis population.
Class I Mutations (Nonsense Mutations):
    * A prominent example discussed is the $G542X$ mutation.
    * In this specific mutation, the DNA sequence at position $542$ is altered. Instead of coding for the amino acid Glycine, it codes for a stop codon.
    * Translation Implications:
        * A normal CFTR polypeptide consists of $1480$ amino acids.
        * In individuals with the $G542X$ mutation, the ribosome stops prematurely, resulting in a truncated protein of only $542$ amino acids.
        * This truncated polypeptide is non-functional because it is missing nearly two-thirds of the necessary amino acid sequence.

Treatment for Nonsense Mutations:
    * The speaker categorizes the pharmaceutical approach for Class I mutations under the term read-through compounds.
    * Mechanism of Action:
        * These compounds target the ribosome during translation.
        * They allow the ribosome to essentially "ignore" or read through the premature stop codon introduced by the mutation.
        * This enables the ribosome to continue adding amino acids and complete the full-length polypeptide chain, potentially restoring function to the CFTR protein.

Question: What is DNA? What kind of molecule is it? It ends in ASE, so what kind of molecule?
Response: It is an enzyme that breaks down DNA by breaking phosphodiester bonds.
Discussion on Testing: The speaker mentions that genetic testing is expensive because of the volume of mutations; his own wife had to undergo this analysis (likely as a carrier screen) to see if she carried any of the $2500$ characterized mutations.